The present invention relates to apparatus for feeding a mixture of steam, gas and air into a rotary kiln under the layer of the material processed, and more specifically into a cement kiln in order to remove, for example, chlorides from the sinter obtained in carrying out the process when these compounds were added to the stock before the sintering thereof or alternatively, to calcinate the sinter in the calcination zone, a mixture of gas and air with steam or without being used in this latter case. The invention may also find utility in the metallurgical and chemical industries as a means of introducing a mixture of gas and air or that of steam, gas and air under the layer of material which must be heat-treated within just one of the process zones a rotary kiln, a drying oven or a cooler for bulk material is subdivided into along its length. In addition, the invention can be used for feeding a mixture of gas and air under the layer of material in stationary equipment for the fluidized-bed treatment of bulk materials.
There is known an apparatus for feeding a mixture of gas and air into a rotary kiln under a layer of material comprising burners which are disposed along the generatrix of the shell of the kiln and admitted into the body whereof is air or a mixture of air and steam. Each burner is provided with a plurality of nozzles wherein the gas is intermixed with the air or steam-air mixture. Each nozzle of each burner is located in the refractory lining of the kiln, consists of a cylindrical portion the outlet wherefrom is provided in the form of converging and diverging cones and accommodates an axially disposed hollow movable rod which is provided with perforations within a portion passing through a gas chamber. The rod is movably linked up with a means of actuation which causes the rod to reciprocate in accordance with a preset programme. The converging and diverging cones are each shaped flat and located in planes running at right angles to each other so that a rectangular slot is formed within the entire length of the outlet from the nozzle. A rake for clearing the slot from granules of material is provided at the end of the rod and extends into the space inside the converging and diverging cones. The gas chamber wherefrom the gas is admitted into the rod is provided inside the nozzle at the inlet therein. All the rods are attached to a common tie beam which is one of the components comprising the means of actuation which causes the rods to reciprocate.
A disadvantage inherent in such an apparatus for feeding a mixture of steam, gas and air into a rotary kiln under the layer of the material processed is that fragments of this material fall down the bodies of those nozzles which are under the layer when the pressure applied to the nozzles ceases to exist due to an interruption in the operation of the draught and blast equipment. The fragments can damage components transmitting the motion from the means of actuation to the rods of the nozzles. The rake each of the perforated rods is provided with is not always capable of clearing the nozzle outlet from fragments of the material. Moreover, if this rake is not centered accurately, the nozzle outlet can be damaged with the sharp edges of the rake with the result that way is opened to more fragments entering the outlet and blocking same as the kiln goes on rotating. The gas outlets provided under the rakes are also likely to be clogged with the material and the same applies to the clearance between each rod and the gas chamber, for neither of these passages is provided with some kind of sealing against the ingress of the spilled material as this shuttles back and forth.
Another disadvantage of the known apparatus is unsatisfactory mixing of the gas with the air in the nozzles, a further disadvantage is damage of the mechanism for cleaning the burners, should one of the rods get stuck in the nozzle, and still another disadvantage is protracted period of starting up the kiln, i.e., the period during which the kiln reaches a steady-state condition. The point is that warming up of the feed to between 650.degree. and 750.degree. C. is required before gas can be admitted into the burners but this temperature is difficult to achieve because the material is cooled by the cold air fed through the burners in great amounts to keep their nozzles unclogged. As a result, the starting-up lasts twice as long as this is commonly the case.
One more disadvantage to be mentioned is the cooling of the leading and trailing portions of the segment the layer of material is shaped like, for cold air is to be admitted into the burners before these enter the layer and after they leave same to prevent any material from falling down the bodies of nozzles, and the gas is admitted only when the layer of material overlaying the burners is between 100 and 300 mm deep or otherwise no complete combustion is obtainable.